Charge pumps may be utilized to provide an output voltage in several different applications. Often, such output voltage may be higher than a supply voltage driving the charge pump. For this purpose, a charge pump may comprise one or more capacitors which are charged to a specific voltage in response to a clock signal. In a first clock phase of a clock signal, the capacitors are connected to the supply voltage, thereby being charged. In a subsequent clock phase, the charged capacitors are coupled to an output terminal providing the output voltage.
Depending on the circuitry of the charge pump, the output voltage can be higher than the external supply voltage applied to the charge pump. Some charge pumps may also comprise additional switching circuitry, thereby achieving a higher flexibility and different output voltage modes. For instance, a charge pump may operate in a 1:1.5 mode or 1:2 mode, wherein in the first output mode, the output voltage of the charge pump is 1.5 times higher than the supply voltage. In the second output mode, the output voltage is two times higher, accordingly.
Clocked charge pumps normally provide an unregulated output voltage. The output voltage of a clocked charge pump can be regulated and particularly regulated to a value greater than an external supply voltage by driving some of the switches in the first phase of the clock cycle accordingly.
Depending on the load coupled to the output terminal of the clocked charge pump, the current drawn from the charge pump may be different. At the same time, switch losses and current leakages due to switching during operation of the charge pump may result in a quiescent current. To reduce such quiescent current, a new operation mode has been proposed, wherein the clocked charge pump is not operated continuously in response to the clock signal. Moreover, the charge pump is operated not continuously; the driving pulses for the charge pump are generated only in specific clock pulses. Such operation called SKIP mode may be dependent on the voltage drop of the charge pump.
When the load connected to the output terminal of the charge pump is low, the charge pump and particularly the switches of the charge pump may consume a lot of power during the switching process leading to a poor efficiency. For that purpose, the pulses driving the switches are selectively deactivated over two or more periods of the clock signal to reduce the power consumption. FIG. 11 shows a typical charge pump designed to be operated in a continuous mode (CONT mode) or in a non-continuous mode (SKIP mode) dependent on the output voltage.
The charge pump according to FIG. 11 comprises a digital signal generation block 920 connected to a driver circuitry 910. The digital signal generation block 920 receives the clock signal and generates all necessary pulse signals for the charge pump. These digital pulses are generated synchronously with a clock signal applied at the clock input. The driver controller 910 has two different functions. First, it provides signals to drive the switches and second, it is used to regulate the maximum output voltage depending on the mode of operation of the charge pump. The several driving signals are applied to the charge pump 900, the charge pump comprising switches and capacitor arrangements being implemented in such way that a clocked operation in response to the clock signal applied to the input terminal of the digital generation block is possible.
Accordingly, the charge pump switches are switching in each cycle of the clock signal. In other words the driving signals are continuously applied to the charge pump.
To change the operation mode, the output voltage Vo is applied to a voltage comparator 940 and compared to a voltage reference signal Vref. The results are received by a skip controller block 930. The skip controller block may prevent the driving signals from being continuously applied to the charge pump in response to the results. Therefore the skip controller block 930 switches the charge pump between a continuous mode of operation and a SKIP mode of operation, respectively.
However, it is possible that the arrangement may stay in the non-continuous mode of operation, even when the output voltage is low but the load applied to the output terminal of the charge pump is high. In such case, the output voltage may comprise high ripples. To prevent to at least reduce such ripples, additional low pass filtering is necessary, which may slow down the available response of the arrangement.